The invention relates to an optical lithographic device with a lens system which has a vertical optical main axis directed parallel to a z-direction and which is fastened to a machine frame of the device, as well as a positioning device which is situated below the lens system and by means of which an object table is displaceable relative to the lens system over a guide surface of a support member coupled to the positioning device, which guide surface extends perpendicular to the z-direction.
An optical lithographic device of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 4,737,823. In this known optical lithographic device, the support member is a rectangular granite slab which forms a base of the machine frame of the device. Four columns of the machine frame extending in the z-direction are fastened on the guide surface which is formed by an upper side of the granite slab. The lens system is fastened to the four columns by means of a horizontal mounting plate at some distance above the granite slab. At a lower side, the granite slab is provided with lower frame supports which are each provided with spring members and damping members. The machine frame of the known optical lithographic device is spring-mounted with low frequency in directions parallel to the z-direction and transverse to the z-direction relative to a bottom surface on which the device is positioned by means of the lower frame supports, a mass spring system formed by the machine frame and the lower frame supports having mechanical natural frequencies of 2 to 4 Hz. The use of the lower frame supports prevents undesirable high-frequency vibrations of the bottom surface being transmitted through the lower frame supports to the machine frame.
A disadvantage of the known optical lithographic device is that the mechanical natural frequencies of the mass spring system formed by the machine frame and the lower frame supports are lower than the frequency of a stepwise movement performed by the object table during operation under the influence of an alternating driving force supplied by the positioning device. An alternating reaction force determined by the driving force and exerted on the machine frame by the positioning device accordingly results in a swinging movement of the machine frame relative to the bottom surface, which adversely affects the accuracy of the optical lithographic device.